title: Polypeptide binding specificities of Saccharomyces cerevisiae oligosaccharyltransferase accessory proteins Ost3p and Ost6p.
abstract: Asparagine-linked glycosylation is a common and vital co- and post-translocational modification of diverse secretory and membrane proteins in eukaryotes that is catalyzed by the multiprotein complex oligosaccharyltransferase (OTase). Two isoforms of OTase are present in Saccharomyces cerevisiae, defined by the presence of either of the homologous proteins Ost3p or Ost6p, which possess different protein substrate specificities at the level of individual glycosylation sites. Here we present in vitro characterization of the polypeptide binding activity of these two subunits of the yeast enzyme, and show that the peptide-binding grooves in these proteins can transiently bind stretches of polypeptide with amino acid characteristics complementary to the characteristics of the grooves. We show that Ost6p, which has a peptide-binding groove with a strongly hydrophobic base lined by neutral and basic residues, binds peptides enriched in hydrophobic and acidic amino acids. Further, by introducing basic residues in place of the wild type neutral residues lining the peptide-binding groove of Ost3p, we engineer binding of a hydrophobic and acidic peptide. Our data supports a model of Ost3/6p function in which they transiently bind stretches of nascent polypeptide substrate to inhibit protein folding, thereby increasing glycosylation efficiency at nearby asparagine residues.
authors.affiliation: School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Queensland 4072, Australia.
authors.forename: M Fairuz B
authors.initials: MF
authors.lastname: Jamaluddin
authors.forename: Ulla-Maja
authors.initials: UM
authors.lastname: Bailey
authors.forename: Nikki Y J
authors.initials: NY
authors.lastname: Tan
authors.forename: Anthony P
authors.initials: AP
authors.lastname: Stark
authors.forename: Benjamin L
authors.initials: BL
authors.lastname: Schulz
mesh_terms: D000595:Amino Acid Sequence; D001216:Asparagine / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites / Q000235:genetics; D055162:Biocatalysis; D006031:Glycosylation; D006602:Hexosyltransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D010455:Peptides / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D008565:Membrane Proteins; D010455:Peptides; D029701:Saccharomyces cerevisiae Proteins; D001216:Asparagine; D006602:Hexosyltransferases; C507060:OST6 protein, S cerevisiae; C025620:dolichyl-diphosphooligosaccharide - protein glycotransferase